Magneto-optic Kerr ellipticity of epitaxial Co/Cu overlayers and superlattices

Co/Cu overlayers and superlattices were grown by molecular-beam epitaxy onto Cu(100) and Cu(111) single crystals. Electron diffraction and Auger spectroscopy were used to characterize the film growth and to confirm the epitaxy. Kerr ellipticities at 633 nm also were measured in situ both for Co overlayers that were 10--500 A{} thick, and for various superlattices as a function of the number of bilayers in the film. The ellipticity data initially increase linearly as a function of total Co thickness, in accord with the additivity law expected for magneto-optic signals in the ultrathin limit. In order to simulate the observed thickness trends, however, it was necessary to assign a value to the complex magneto-optic coupling constant that differs from those reported previously.